Microbial growth occurs in many systems in which aqueous media such as water, aqueous solutions and aqueous dispersions are employed.
For example, significant biofouling can occur in many areas of photoprocessing systems and, in particular, where low flow rate washes and water recycling is used. The problem may be overcome by adding biocides to the wash water tanks when bacterial biofilm formation becomes evident visually. However at this point the biocides may not work and even at quite high concentrations are not particularly effective because the bacteria have attached to surfaces to form colonies which have built up in layers. Hence, any biocide in solution can only reach the outer biofilm layer and not the inner layers of the biofilm which are protected. Furthermore, widespread use of such biocides is not desirable because they are relatively expensive and toxic chemicals which require specialised disposal to protect the environment.
Alternative methods of inhibiting bacterial growth in aqueous media involve the gradual release of a biocide through interaction with water e.g. by leaching.
U.S. Pat. No. 4,552,591 describes a biocidal composition for inhibiting microbial growth in oil field waters which comprises a biocide and a solid, particulate adsorbent therefor. The biocides are conventional water soluble compounds traditionally used in the treatment of oil field waters e.g. 2-methyl-4-isothiazolin-3-one which are adhered to a known adsorbent e.g. diatomaceous earth. The compositions avoid the personal and environmental contamination which can result from spillage of the biocide used previously in liquid form. After addition to oil field waters, such compositions release the biocide through leaching.